With avian influenza in the news recently, I’ve been thinking a lot about infectious diseases humans can catch from contact with infected animals. In the past few decades, the number of known “zoonotic”diseases – those passed from animals to humans – has dramatically increased.

Many zoonotic diseases can be prevented by being careful about how we prepare our food and water.

Cooking eggs and meat – beef, poultry and pork – thoroughly decreases the likelihood of infection with gastrointestinal infections such as salmonella, shigella, E. coli and tapeworms (though does not reduce the risk of acquiring bovine spongiform encephalopathy, also called mad cow disease).

Cooking fish and shellfish thoroughly destroys the hepatitis A virus, tapeworms, roundworms and other bacteria and viruses that can cause gastrointestinal infections.

The practice of pasteurizing milk kills microorganisms that cause tuberculosis, brucellosis, Q fever and other milk-borne diseases.

Treating water by boiling, chlorination or filtration all but eliminates the chances of human infection with typhoid fever, giardia, cryptosporidium, shigella and E. coli. In underdeveloped countries without a safe water supply, these diseases affect large numbers of humans, causing suffering as well as negative economic impact.

Consuming food that has been contaminated by animal diseases is only one way of contracting zoonotic infections.

Avian influenza – bird flu – is transmitted when humans have direct contact with infected birds, bird feces or contaminated surfaces. The greatest worry this flu season is that the avian influenza virus will mutate so that it can also be easily transmitted from person to person.

So far, domestic and wild birds across Asia and into Eastern Europe have been found to be infected with this H5N1 avian influenza virus. It is possible that migrating birds will spread the virus to other areas. Human cases were reported in four countries: Cambodia, Indonesia, Vietnam and Thailand as of mid-November.

In the Pacific Northwest, a recent case of hantavirus in a Morrow County farmworker is an example of a zoonotic infection passed from rodents to humans. Hantavirus pulmonary syndrome occurs when a human inhales the virus, found in rodent droppings, urine and saliva. For this reason, use caution when cleaning up dead rodents, rodent nests or droppings. Do not sweep or otherwise stir up the area; instead, wet the area with bleach and water solution before cleaning up. Make sure the area is well ventilated and wear gloves.

According to Emilio DeBess, public health veterinarian, “Hantavirus cases are rare both in Oregon and around the nation.”

Oregon has reported six cases since 1996.

People can be infected by inhaling concentrated virus particles that become airborne when rodent droppings or nests are disturbed.

The first signs of illness appear one to six weeks after exposure to the virus. Early symptoms include fatigue, fever and muscle aches, which may progress to coughing and shortness of breath as lungs fill with fluid.

The primary way to protect yourself from Hantavirus is to control rodents and keep them from nesting in and around the home or workplace.

Tularemia (“rabbit fever”) is a zoonotic disease, carried by wild rabbits and other rodents. People can be infected if they handle infected animals, eat infected rabbit meat or are bitten by a tick or deerfly that has bitten an infected animal.

Rabies is another zoonotic disease that can be passed from infected mammals to humans via a bite or other contact with the animal’s saliva. Animals such as raccoons, bats, skunks, foxes, coyotes, dogs and cats can all carry the rabies virus.

Pregnant women and immunosuppressed people are at highest risk of infection with toxoplasmosis, a disease that house cats can carry and pass to humans through their feces.

Infants, children and anyone with a suppressed immune system are at higher risk of acquiring salmonella from pets, especially lizards, snakes, turtles, baby chicks and ducklings. These animals pass salmonella in their feces, so it’s important to wash your hands well after contact with animals. Salmonella causes fever, diarrhea and stomach pain, and can be very serious.

The list of zoonotic diseases transmitted to humans by insects is long. Mosquitoes in tropical regions carry some of the most serious diseases, such as malaria, dengue fever and Japanese encephalitis. In the United States, mosquitoes carry West Nile virus and several types of encephalitis. Ticks can infect humans with Lyme disease, relapsing fever, Rocky Mountain spotted fever and several other zoonotic diseases.

Kathryn B. Brown is a family nurse practitioner with a master’s degree in nursing from OHSU.